Due to the inherently finite nature of fossil fuel resources, the world faces the challenge of finding suitable renewable substitutes that can begin to replace petrochemicals both as a source of energy and as a source of materials for plastics, rubbers, fertilizers, and fine chemicals. More recently, biofuels have been endorsed as a key component of national and international strategies to reduce greenhouse gas (GHG) emissions and mitigate potential climate change effects.
Two biofuels, ethanol (ethyl alcohol) and biodiesel from fatty acid methyl esters account for the vast majority of global biofuel production and use today. These biofuels are made primarily from agricultural commodities, such as grain and sugar cane beet molasses, cassava, whey, potato and food or beverage waste for ethanol and vegetable oil for biodiesel.
In 2010, approximately 87 billion liters (23 billion gallons) of ethanol were produced, with the United States, Brazil, and the European Union accounting for 93% of this output (RFA, 2011a), which leaves large quantities of DG byproducts, mainly used for animal feeds. Two processes are primarily used to make ethanol from grains: dry milling and wet milling. In the dry milling process, the entire grain kernel typically is ground into flour (or “meal”) and processed without separation of the various nutritional component of the grain. The flour is slurred with water to form a “mash”. Enzymes are added to the mash, which is then processed in a high-temperature cooker, cooled and transferred to fermenters where yeast is added and the conversion of sugar to ethanol begins. After fermentation, the resulting ethanol containing mixture “beer” is transferred to distillation columns where the ethanol is separated from the residual “stillage”. The stillage is sent through a centrifuge that separates the solids from the liquids. The liquids, or solubles, are then concentrated to a semi-solid state by evaporation, resulting in condensed distiller's solubles (CDS) or “syrup”. CDS is sometimes sold direct into the animal feed market, but more often the residual coarse grain solids and the CDS are mixed together and dried to produce distiller's dried grain with solubles (DDGS). In the cases where the CDS is not re-added to the residual grains, the grain solids product is simply called distiller's dried grain (DDG). If the distiller's grain is being fed to livestock in close proximity to the ethanol production facility, the drying step can be avoided and the product is called wet distiller's grain (WDG). Because of various drying and syrup application practices, there are several variants of distiller's grain (one of which is called modified wet distiller's grain), but most product is marketed as DDGS, DDG or WDG. Some dry-mill ethanol plants in the United States are now removing crude maize oil from the CDS or stillage at the back end of the process, using a centrifuge. The maize oil is typically marketed as an individual feed ingredient or sold as a feedstock for further processing (e.g. for biodiesel production). The co-product resulting from this process is known as “oil extracted” DDGS or “de-oiled” DDGS. These co-products typically have lower fat content than conventional DDGS, but slightly higher concentrations of protein and other nutrients. A very small number of dry-mill plants also have the capacity to fractionate the grain kernel at the front end of the process, resulting in the production of germ, bran, “high-protein DDGS” and other products (RFA, 2011b). In some cases, ethanol producers are considering using the cellulosic portions of the maize bran as a feedstock for cellulosic ethanol. The majority of grain ethanol produced around the world today comes from the dry milling process. In the wet milling process, shelled maize is cleaned to ensure it is free from dust and foreign matter. Next, the maize is soaked in water, called “steepwater”, for between 20 and 30 hours. As the maize swells and softens, the steepwater starts to loosen the gluten bonds with the maize, and begins to release the starch. The maize goes on to be milled. The steepwater is concentrated in an evaporator to capture nutrients, which are used for animal feed and fermentation. After steeping, the maize is coarsely milled in cracking mills to separate the germ from the rest of the components (including starch, fibre and gluten). Now in a form of slurry, the maize flows to the germ separators to separate out the maize germ. The maize germ, which contains about 85% of the maize's oil, is removed from the slurry and washed. It is then dried and sold for further processing to recover the oil. The remaining slurry then enters fine grinding. After the fine grinding, which releases the starch and gluten from the fibre, the slurry flows over fixed concave screens which catch the fiber but allow the starch and gluten to pass through. The starch-gluten suspension is sent to the starch separators. The collected fibre is dried for use in animal feed. The starch-gluten suspension then passes through a centrifuge where the gluten is spun out. The gluten is dried and used in animal feed. The remaining starch can then be processed in one of three ways: fermented into ethanol, dried for modified maize starch, or processed into maize syrup. Wet milling procedures for wheat and maize are somewhat different. For wheat, the bran and germ are generally removed by dry processing in a flour mill (leaving wheat flour) before steeping in water.
In 2010, an estimated 142.5 million tonnes of grain was used globally for ethanol (F.O. Licht, 2011), representing 6.3% of global grain use on a gross basis. Because roughly one-third of the volume of grain processed for ethanol actually was used to produce animal feed, it is appropriate to suggest that the equivalent of 95 million tonnes of grain were used to produce fuel and the remaining equivalent 47.5 million tonnes entered the feed market as co-products. Thus, ethanol production represented 4.2% percent of total global grain use in 2010/11 on a net basis. The United States was the global leader in grain ethanol production, accounting for 88% of total grain use for ethanol. The European Union accounted for 6% of grain use for ethanol, followed by China (3.4%) and Canada (2.3%). The vast majority of grain processed for ethanol by the United States was maize, though grain sorghum represented a small share (approximately 2%). Canada's industry primarily used wheat and maize for ethanol, while European producers principally used wheat, but also processed some maize and other coarse grains. Maize also accounted for the majority of grain use for ethanol in China.
There is huge existing market of wood glue for wood panel industry. Organic polymers of either natural or synthetic origin are the major chemical ingredients in all formulations of wood adhesives. Urea-formaldehyde is the most commonly used adhesive, which can release low concentrations of formaldehyde from bonded wood products under certain service conditions. Formaldehyde is a toxic gas that can react with proteins of the body to cause irritation and, in some cases, inflammation of membranes of eyes, nose, and throat. It is a suspected carcinogen, based on laboratory experiments with rats.
Phenol-formaldehyde adhesives, which are used to manufacture plywood, flakeboard, and fiberglass insulation, also contain formaldehyde. However, formaldehyde is efficiently consumed in the curing reaction, and the highly durable phenol-formaldehyde, resorcinol-formaldehyde, and phenol-resorcinol-formaldehyde polymers do not chemically break down in service to release toxic gas. However, it uses the petroleum-based resource and also expensive.
Increasing environmental concerns and strict regulations on emissions of toxic chemicals have forced the wood composites industry to develop environmentally friendly alternative adhesives from abundant renewable substances such as soybean protein, animal, casein, vegetable, and blood. Also, adhesives from lignin, tannin, and carbohydrates have been studied for replacement of synthetic adhesives that are dominatingly used in the manufacture of wood composite products. These adhesives are generally used for non-structural applications, due to their poor water resistance and low strength properties.
Modifications including further purification to obtain high protein contents, increases of the specific surface area of the materials, denaturation of the protein by acid, alkaline and surfactants have been shown to be useful to enhance the wood adhesive strength of soy based glue, or mixed with other synthetic adhesives such as phenol formaldehyde resin which increase the cost for manufacturing.
It would, therefore, be advantageous to provide renewable bio-adhesives which are able to be used as wood adhesives with comparable strength as the synthetic wood adhesives such as formaldehyde based glue.
It is, therefore, a primary objective of the present invention to provide a stable adhesive generally inexpensive and versatile.
It is, therefore, a further object of the present invention to provide a stable aqueous adhesive comprising DG-material derived from ethanol production, and that are safe, water-resistant for wood application. The DG materials include DDGS, CDS, DDG and WDG from byproducts of ethanol production plant.
It is a further object of the present invention to prepare DG based adhesive products that are produced by mixing dry DG materials with additives and further milled into fine powder for greater adhesive strength properties to broaden their suitability for adhesive applications, easy in storage for longer shelf-life and transportation.
It is yet a further objective of the invention to prepare DG based adhesive products that are produced by mixing dewatered DG materials, e.g. WDG and CDS (water content less than 70%) with additives and homogenised into aqueous bio-adhesives.
It is yet a further object of the invention to prepare an adhesive that consists essentially of byproducts of after ethanol distillation during ethanol biofuel process.
It is yet another object of the invention to prepare adhesive products that comprise naturally DG materials in dry form (e.g. DDGS and DDG) that are blended with a crosslinking agent to form a crosslinked network to enhance the water resistance of the adhesives.
It is further another object of the invention to mill the above mixture to greater than 80 meshes for formulation into aqueous adhesives.
It is yet another objective of the invention to prepare adhesive products that comprise above aqueous adhesives and a crosslinking agent and/or wet-strengthen agent for water-resistant wood industry application.